This invention relates to roller circles for hoisting and excavating equipment and the like, and particularly to an improved roller circle using tapered rollers and a mechanism for accommodating the radial thrust loads to which the rollers are subjected
Rollers circles are used to support a revolving framework upon a relatively stationary lower works. The revolving frame may mount excavating or hoisting equipment while the lower works is either stationary or adapted to travel from location to location for operation of the hoist or excavating equipment.
Particularly among larger machinery, it is typical to use tapered rollers whose axes of rotation are arranged radially relative to the center of rotation of the rotary frame and which rollers are in rolling contact with bearing surfaces of upper and lower annular rails. The lower rail is attached to the lower relatively stationary works, while the upper rail is attached to the revolving frame.
On large earth moving excavators such as draglines, shovels, wheel excavators, and other assortments of rotating machinery, the base or lower works of the machine rests stationary on the ground while the machine is in operation. The upper works of the machine that is mounted to the upper revolving frame is free to rotate to align the digging structure such as a boom and suspended bucket, or a boom handle and dipper. The roller circle supports the vertical loads resulting from the dead weight of the upper works and the live loads induced while digging, dumping, transferring, and so forth. Horizontal forces caused by the operation of the equipment are carried by a center pintle or pin. The center pin is usually mounted as part of the lower works and is connected to the upper works through a bearing or bushing to center the upper works to the lower works while the machine is rotated.
The typical roller circle consists of a large quantity of individual rollers that are pinned to rolled plates that serve as inner and outer cage frames. The cage frames maintain the spacing between adjacent rollers and align the axes of the rollers. The rollers ride on segmented rails. The lower rail is typically a continuous 360.degree. while the upper rail may be continuous or partial. To provide a smooth rolling action and to prevent skidding of the rollers, tapered rollers in the form of truncated cones are used. Bearing surfaces are provided on the rails that mate with the tapered rollers. The taper is such that the upper and lower lines of rolling contact of the rollers cross at a common vertex on the center line of rotation of the revolving frame.
When a vertical load is applied to a tapered roller, the taper will induce an axial thrust load that will tend to squeeze the roller to the outside, away from the center line of rotation. The roller must be restrained axially to maintain its proper alignment with the upper and lower rails. Several methods of axially restraining the roller have been proposed in the past. In one method, the roller is provided with an integral flange on its internal smaller end. The flange contacts the inside edge of a rail which thereby restrains the roller from moving axially to the outside. A second integral flange on the outer larger end of the roller may be used in addition. The second flange provides additional security to keep the rollers in place while also providing a restraint to prevent the revolving frame from shifting off of the roller circle. Another approach uses an additional rail that engages the roller to the outside of the roller circle to carry the thrust load from the roller. An example of this latter approach is found in U.S. Pat. No. 4,582,436 issued Apr. 15, 1986, to Merron.